1. Field of the Invention
The invention relates to a vessel that can be filled with liquid and closed in pressure-tight condition, and from which liquid can be withdrawn. Examples of such vessels are drums, small drums (party kegs) or cans, in which CO2-containing liquids, especially beverages, are filled under pressure. In particular, it relates to party beer kegs.
2. Description of Related Art
There exist tap fittings that operate with high-pressure CO2 cartridges and that can be used to tap such vessels in order to withdraw liquid therefrom by means of CO2 pressure. This corresponds to the standard tapping technique in gastronomy, wherein CO2 from high-pressure CO2 bottles is used and very good wholesomeness and shelf life of the beer are achieved.
In some consumer groups, however, tap fittings with CO2 high-pressure cartridges have not become popular. For persons who buy party beer kegs only occasionally, it is not worthwhile to procure an expensive tap fitting. Some people are even uncomfortable handling high-pressure CO2 cartridges. Others worry about the replacement supply of cartridges.
There have therefore been developed party beer kegs equipped with an integrated outlet tap in the bottom region of the keg, whereby the beer can be drawn by the internal pressure and gravity alone. Usually air is admitted to the party keg above the liquid surface therein, in order to permit pressure equalization. This can be achieved by puncturing with a can opener. However, other party beer kegs have an integrated outlet tap and a hand-operated air-admission valve in the top end plate of the keg, forming part of a bunghole closure (see WO 99/23008 A1).
A disadvantage of such party kegs is that the wholesomeness and shelf life of the beer are impaired by the ingress of air into the top space of the keg. When a party keg of this type is tapped, the contents must be consumed quickly, so that the beer does not become flat and stale.
Several suggestions have been made as regards improving the shelf life of beer in a tapped party keg. For example, WO 99/47451 A1 teaches integrating an aerosol can that contains CO2 bound to active carbon under low pressure into the party keg and building up a CO2 pressure in the top space of the keg sufficient to equal or exceed the partial pressure of the CO2 dissolved in the beer. A disadvantage is the large volume of the can. Furthermore, active carbon is a very expensive storage medium.
From DE 19952379 A1 there is known a CO2 dispenser for party kegs in the form of a separate manual device, with which the party keg is pierced above the liquid surface therein in order to pump CO2 into the top space of the keg. The dispenser contains a high-pressure CO2 cartridge and a pressure-regulating valve. It is intended for multiple uses and can be transferred from party keg to party keg. Even if the CO2 consumption may be smaller than in the case of a tap fitting operating with CO2, such a CO2 dispenser ultimately raises similar concerns in consumer groups.
From practice it is also known that there can be introduced into the top space of a party beer keg a pressure bag, which expands when the pressure in the top space drops, thereby on the one hand filling the empty space being formed and on the other hand exerting a contact pressure on the liquid surface in the keg greater than the partial pressure of the CO2 dissolved in the beer. The pressure bag comprises multiple plies of plastic film that is impermeable to oxygen diffusion. It has a plurality of chambers that contain gas-forming chemicals, such as baking powder and citric acid. The chambers are successively activated as the pressure drops in the top space of the party keg and are inflated by the gas evolved during the reaction of the chemicals.
A disadvantage of the known pressure bag is the unsteady application of pressure on the beer. The pressure rises suddenly when the respective next chamber of the pressure bag is activated, and it then drops successively. This results in irregular tap behavior. The tap behavior fluctuates between discharge of the beer in a strong stream and a mere trickle.
The starting point of European Patent Application No. 05011896.7 is to provide a vessel of the type mentioned hereinabove having an integrated compressed CO2 gas source of small overall volume, from which discharged CO2 exerts a steady pressure on the liquid in the vessel and improves its shelf life and wholesomeness. The vessel has an insert that can be fixed in sealed manner in an opening of the vessel and a high-pressure CO2 cartridge, a pressure-regulating valve for discharging CO2 therefrom and a control element that is accessible from the outside and that can be actuated to pierce the high-pressure CO2 cartridge with a piercing needle.
By virtue of its small overall volume, the insert is suitable for replacing the bunghole closure with pressure-equalizing valve according to WO 99/23008 A1, without necessitating any substantial modifications to the shape and size of the respective vessel to be equipped therewith, such as a party beer keg. The processes at a filling plant are altered slightly at most. The insert can be made of plastic materials, which for years have proved most suitable for a bunghole closure with pressure-equalizing valve and an outlet tap. The operation of the compressed CO2 gas source can be designed such that a user familiar with actuation of a conventional pressure-equalizing valve hardly notices any difference. The user does not directly handle a high-pressure CO2 cartridge, which would probably make him uncomfortable. The cartridge is designed for one-time use in a single vessel and will be disposed of together therewith. In particular, the shelf life of beer in a tapped party keg will be extended by several days without concern by filling the top space with CO2 instead of air.
Commercial pierceable CO2 cartridges in a size suitable for the compressed CO2 gas source contain approximately 16 g of CO2 at a pressure of approximately 80 bar. The reduction and precise regulation of the pressure of the CO2 discharged into the top space of the vessel imposes considerable requirements on the construction of a compressed CO2 gas source in the form of a compact insert. The pressure is typically between 0.5 and 0.9 bar. It is equal to or slightly higher than the partial pressure of the CO2 dissolved in the liquid.
Especially for beer, the CO2 content is one of the factors that determines the taste. The CO2 content varies from beer variety to beer variety. If the CO2 pressure in the top space of the party keg is too low, CO2 escapes from the beer. If the CO2 pressure in the top space is too high, the beer becomes overcarbonated and its taste and wholesomeness are impaired. The compressed CO2 gas source described in European Patent Application No. 05011896.7 ensures that neither one nor the other occurs.
In the vessel according to European Patent Application No. 05011896.7, the control element actuated to pierce the high-pressure CO2 cartridge is a rotary knob, which cooperates with an axially guided slide used to actuate a piercing needle. The piercing needle is structurally combined with a valve element of the pressure-regulating valve. Its regulating function may be adversely affected if the user actuates the rotary knob once again. Certainly this is completely undesirable, but in the vessel according to European Patent Application No. 05011896.7 it is not precluded.